In common with most sports followers, GAA fans like to mimic their heroes. The typical supporter now owns at least one replica jersey, and may even wear the "away" strip when required.
He often sustains himself during games with sports drinks of the kind that allegedly keep top athletes going 33 per cent longer. Sometimes it is only his finely honed beer belly that suggests a lifestyle less committed than the team's.
But apart from one of them not being super-fit, there is another key difference between the GAA fan and the player. Unlike the latter, the former never shakes hands with his opposition before a game. Afterwards, yes. It is part of the GAA code that come the final whistle, win or lose, opposing supporters must offer each other the sign of peace, along with best wishes for the future. But never in advance.
Partly this is because, as a supporter, it usually takes the first 15 or 20 minutes to find out who your "marker" is. There may be a number of opposition fans equidistant from you; and besides, in the early stages of a game, exchanges are often just good-humoured banter.
Then, gradually, somebody around you will start getting on your nerves. From here on, this is your man (I'm using male-gender terms for convenience: the offender can just as easily be female). Your job for the rest of the game is to annoy him at least as much as he's annoying you.
At the Kerry-Monaghan match on Sunday, my marker was obvious from the moment I sat down. Kerry fans are not the worst, by any means. In fact, in my experience, they are among the least offensive GAA supporters, because - typically - they don't attend the match at all. That is to say, they don't attend the sort of matches Monaghan are involved in. They wait for finals instead.
But not only was this Kerry fan here - right in front of me - he was also wearing a humorous green-and-gold wig. That was two crimes, even before the ball had been thrown in. I didn't have to wait for him to applaud loudly all the referee's more misguided decisions (ie. the ones in favour of Kerry), as he subsequently did. It was clear from the start that he would be my responsibility.
I was even tempted to gain a psychological edge by introducing myself straight away and making some disparaging comment (eg: "that wig really suits you"). But out of respect for tradition, I held back. I would wait for Monaghan to start playing Kerry off the pitch - a high-risk strategy, admittedly - and then sicken him with enthusiasm.
Painful as it can be at times, the lack of segregation at matches is one of the glories of the GAA. And even the pain - when your team loses and there are celebrations all around - can be character-building.
Down the years, Kerry supporters have not had nearly enough of these opportunities for growth. But as the game unfolded on Sunday, it looked like this was going to be one of them. The man in front could not have accused me of being exactly triumphalist at any stage of the match. In fact, historically, the words "triumphalist Monaghan supporter" have been a contradiction in terms. Yet for most of the 70 minutes, I was definitely annoying him more than he was annoying me.
The key moment appeared to have come mid-way through the second half when Kerry full-forward Kieran Donaghy caught a high ball, turned, and rifled a shot into the side-netting.
Whereupon, the supporter in front turned almost as quickly and, facing me for the first time, celebrated what he thought was a goal. I broke the news to him - not as gently as I might have, perhaps - that the ball had gone wide. And if schadenfreude were a variety of cigar, I would have lit one there and then and blown smoke-rings at him.
But of course soon after, his team did score a goal, ensuring that Monaghan entered the game's dying stages without the sort of lead that little teams need in tight finishes against big ones. Our heroes had beaten the Kerry selection that started the game. They just couldn't beat their bench. The lead disappeared and, from years of experience, the green-and-gold supporters could smell our fear now.
Still, it was a point of pride to keep shouting until either the final whistle or laryngitis intervened. When Kerry cruelly chose the game's last minute to take the lead for the first time, even the man in front seemed too embarrassed to cheer.
Yesterday's newspapers reported that there were "a number of larcenies" during the three days of Puck Fair, which ended on Sunday night. This was no surprise to me. I witnessed one of the worst incidents: in which a gang of 15 men - all believed to have addresses in Kerry - robbed an innocent Monaghan team of a match that was rightfully theirs.
It was all over now bar the handshake, before which I had to compose myself for a few moments. In the event, the Kerry supporter pre-empted me, turning around and offering his hand first. I didn't even catch what he said: the lump in my throat had begun to affect my hearing. But it was something apologetic - maybe "sorry for your trouble".
He was so dignified in victory, as Kerry supporters tend to be, that I no longer even noticed his wig.